This invention relates to new compositions and to improvements in the electrodeposition of copper from aqueous acidic copper plating baths, preferably from aqueous acidic copper plating baths containing one or more bath-soluble copper salts, free acid and chloride ions.
Acid copper plating baths for producing a brilliant copper finish on articles have been known in the art, and a number of patents have described various brightening agents which can be added to acidic baths. Examples of such patents include U.S. Pat. Nos. 2,707,166; 2,707,167, 2,830,014; 3,276,979 and 3,288,690. In U.S. Pat. No. 3,725,220, it has been suggested that the utilization of organic sulfonates or carboxylates as brightening additives in acid aqueous copper plating baths results in improved stability of the bath and effective deposition of copper over a satisfactory current density range.
In a number of instances in the prior art acid copper plating baths, a sufficiently brilliant finish is obtained but little or no smoothing effect on the surface is obtained. The ability of a plating bath to produce deposits relatively thicker in small recesses and relatively thinner on small protrusions thereby decreasing the depth of surface irregularities is known as "leveling."For example, a copper plating bath with satisfactory leveling ability can be utilized to reduce or eliminate the effect of microscopic cracks or scratches on the surfaces of the articles being plated. Accordingly, a number of additives have been described in the prior art for increasing the leveling effect of acid copper plating baths. For example, U.S. Pat. No. 3,101,305 describes a leveling additive obtained from the condensation of thiourea with aliphatic aldehyde such as formaldehyde. Since the additives which have been described in the prior art are useful either as brightening agents or leveling agents, it generally has been necessary to utilize two additives in acid copper plating baths, one for brighteners and another for leveling. U.S. Pat. No. 4,038,161 is an example of a patent which describes the use of two additives in acid copper plating baths. One type of brightener compound disclosed in U.S. Pat. No. 4,038,161 to be used in combination with a leveling agent is the dithiocarbamic acid derivatives of the formula EQU R.sub.1 R.sub.2 NCS.sub.2 --(CH.sub.2).sub.n --X
wherein R.sub.1 and R.sub.2 are hydrogen, aliphatic or aromatic groups, n is an integer from one to ten, and X is a hydroxyl group, a carboxyl group, a sulfonic acid group or an alkali metal salt of the carboxyl or sulfonic acid groups. U.S. Pat. No. 3,414,493 also describes brightener compositions for copper plating baths, and one of the types of brightener composition can be presented by the formula EQU R.sub.3 R.sub.4 NCS.sub.2 CH.sub.2 O(CH.sub.2).sub.n SO.sub.3 M
wherein R.sub.3 and R.sub.4 are alkyl radicals, n is an integer from 3 to 8, and M is hydrogen, sodium or potassium.